HV has two power sources: engine and motor. According to the connecting method, HV propulsion systems may be classified into three forms: series, parallel and series-parallel.
A series propulsion system refers to that the engine directly drives the dynamo to supply electricity to the energy storing device and motors and the motors drive the vehicle to run. A parallel propulsion system refers to that the engine and the motors may drive the vehicle separately and jointly.
The driving modes of series propulsion systems and parallel propulsion systems are relatively singular and do not have the advantages of a hybrid propulsion system, so series-parallel propulsion systems are used normally at present. A series-parallel propulsion system refers to that the engine and the motors are coupled together via a speed-change mechanism, thereby the relations between the rotate speed of the engine and the motors can be regulated according to the running condition. Compared with a series propulsion system and a parallel propulsion system, a series-parallel propulsion system may more flexibly regulate the power output of the engine and the operation of the motors according to the operating condition.
In a conventional series-parallel propulsion system, the power coupling between the engine and motors is generally realized via a speed-change mechanism. However, the speed-change mechanism typically adopted by a conventional series-parallel propulsion system has a large volume and is not convenient for the arrangement of the components of HV. Further, a conventional series-parallel propulsion system does not give full consideration to the power distribution among the engine and the motors and is unable to ensure the engine and motors are in a desirable state in different operating conditions to obtain higher output power.
Therefore, a pressing technical problem in the art is how to realize a compact structure and desirable power distribution among the engine and the motors for a conventional HV.